Excessive use of chemical insecticides to control Spodoptera frugiperda in maize (Zea mays L.) crops in Colombia has resulted in pest resistance and environmental contamination. A Colombian multicapsid nucleopolyhedrovirus (SfMNPV) was produced in laboratory reared larvae and formulated as a wettable powder by microencapsulating the viral occlusion bodies (OBs) with a methacrylic acid polymer. Microencapsulated OBs were tested for insecticidal activity in laboratory, greenhouse and field bioassays, and were then sprayed onto a commercial crop where their effect on arthropod populations was estimated. In laboratory bioassay, microencapsulated and non-microencapsulated OBs caused a larval mortality of 98 and 96%, respectively. The percent of plants showing recent feeding damage in a greenhouse experiment oscillated between 2.5 and 7.5% when OBs were applied compared to 70% observed in the control. In two field trials, the highest dose of 1.5×10¹² OBs/ha (1500 g/ha) was selected as the recommended rate for field application in maize crops, with efficacies higher than 70%. Total arthropod populations were negatively affected by chemical pesticides; whereas the OBs formulation did not affect the diversity of these organisms. Our results indicate that microencapsulated SfMNPV has the potential to be commercialised as an alternative to substitute or complement chemical insecticides in fall armyworm integrated management programmes.

The ability of the isolate VG008 of S. frugiperda granulovirus (SpfrGV) to enhance the infectivity of the isolate SfCOL of S. frugiperda multiple nucleopolyhedrovirus (SpfrMNPV) was evaluated on S. frugiperda larvae. Bioassays were performed with mixtures by using different proportions 90%:10% (M1), 95%:5% (M2) and 97.5%:2.5% (M3) of SfCOL:VG008, respectively. All mixtures showed higher insecticidal activity that SfCOL. The mixture M3 showed the highest enhancement of SfCOL reducing 11.40 times the Mean Lethal Concentration and 96 h in the Mean Time to Death. The enhancer activity of proteins derived from VG008 (GVPs) were also evaluated in mixture with SfCOL. The GVPs increased 27% larval mortality caused by SfCOL and damaged the peritrophic membrane of S. litura larvae, suggesting that the key point in this enhancing activity is the initial step of the larva colonization, the midgut infection. M3 was formulated and evaluated under greenhouse conditions in maize plants using different doses. The highest efficacy was obtained with the highest dose of M3 (8 × 10¹¹ OBs/ha), which was similar to that found when formulated SfCOL was applied using an approximately twofold higher dose. The viral mixture M3 was selected as the active ingredient for developing a new biopesticide for a more efficient management of the pest in the field.

Background: The fall armywormSpodoptera frugiperdais one of the major pests in maize crops, causing important production losses. The pest has rapidly spread worldwide, generating an urgent need to develop efficient and sustainable strategies for its control. In this work, the potential of integrating nucleopolyhedrovirus- (NPV) and the fungusMetarhizium rileyito controlS. frugiperdalarvae was evaluated under laboratory, greenhouse, and field conditions.Methods: The mortality ofS. frugiperdalarvae was evaluated after the application of NPV andM. rileyialone or in combination using three concentrations (high, medium and low) under laboratory conditions. Then, two greenhouse trials using maize plants were carried out to evaluate the effect of individual or combined applications of NPV andM. rileyionS. frugiperdamortality (first trial) and fresh damage (second trial). Finally, a trial under field conditions was conducted to evaluate the performance of the treatment selected in the greenhouse assay.Results: The combined use of NPV:M. rileyiapplied simultaneously showed an additive effect in laboratory, causing higher larval mortality than the biocontrol agents used separately. This effect was evident in the mixtures using the concentration levels high:medium, medium:medium, and medium:high. Under greenhouse conditions, the use of a 50:50 ratio of the two entomopathogens also caused higher larval mortality and a significantly reduced insect damage to plants. Finally, under field conditions, the individual or sequential application of NPV andM. rileyiusing 100% of their recommended doses, and the simultaneous application of both entomopathogens at 50% of their recommended doses, significantly reduced the recent foliar damage to levels under the threshold for economic losses (30% fresh damage) while the damage reached 43% when control measures were not used.Conclusion: The combined application of NPV andM. rileyi(two biocontrol agents with different mode of action) demonstrated an additive effect that allows to reduce to half their recommended application doses. In this context, the integration of both entomopathogens is a promising strategy to manageS. frugiperda,contributing to improve the economic feasibility of biological control tools for the sustainable fall armyworm management.

Wettable powder formulations by microencapsulation of viral occlusion bodies (OBs) of both Spodoptera frugiperda multiple nucleopolyhedrovirus from Colombia (SfCOL) and a genotypic variant (SfCOL-A) were evaluated for controlling the fall armyworm S. frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) in maize crops. Microencapsulation preserved OBs activity after three months of storage at 35ºC, where insecticidal activity loss was not greater than 12%. Additionally, the formulation protected the OBs against inactivation caused by UV-B radiation, retaining its insecticidal activity after 6 hours of UV laboratory exposure, in contrast to unformulated viral suspensions, which presented an Original Activity Remaining (OAR) between 12.1 and 50%. Under greenhouse conditions, the insect mortality was greater than 80% with microencapsulated viruses. In field trials, treatments reduced the percentage of damaged plants to levels below the economic injury level (35%) when the formulated and unformulated virus were applied at 8x1011 OBs/ha (800g/ha) dose, while the damage in the control treatment was close to 60%. Microencapsulation of SfCOL and SfCOL-A OBs provides useful advantages related to half-life and photostability.